1. Field of the Invention
The invention relates generally to downhole tools which are actuated using hydrostatic pressure.
2. Description of the Related Art
A number of downhole tools rely upon total hydrostatic pressure in order to be actuated. Wellbore hydrostatic pressure and applied fluid pressure are used to rupture a frangible member and/or act upon a piston. The wellbore hydrostatic pressure is the pressure exerted by the weight of fluid above a point of interest in the wellbore. Applied fluid pressure is the pressure that artificially applied at surface by a fluid pump. Total pressure is the sum of both wellbore hydrostatic pressure and applied pressure. Hydrostatic setting tools are used to set or actuate a neighboring downhole tool, such as a packer or lock. A commercially available tool of this type is the Striker™ setting tool that is available commercially from Baker Hughes Incorporated of Houston, Tex.
Increasing depth within the wellbore increases the hydrostatic wellbore pressure and, thus, the total pressure differential across a frangible member, such as a rupture disc, also increases. Thus, a setting tool that is useful at a shallower depth may not be useable at a greater depth. As a result, custom setting tool designs having stronger frangible members have to be developed to be used at greater wellbore depths.